1. Field of the Invention
The present invention relates generally to the field of lead acid batteries, and more particularly, to a unique battery grid construction having a center lug. Still more specifically, the present invention relates to positive or negative battery plates made from such center lug grids. The invention also relates to cast-on straps of a unique design which permits materials cost savings, improved conductivity and manufacturing efficiencies in the assembly of the battery elements. In a further refinement of the present invention, the invention relates to grid constructions which include grid lugs having expanded bases and which concentrate metal, typically lead alloys, in the area of the lug to facilitate current collection. In combination, the present invention permits the elimination of individual battery plates or altering the size of the plates, yielding lighter weight batteries having performance characteristics similar to the heavier batteries which they are designed to replace or batteries of similar weight having dramatically improved performance characteristics.
2. Description of Prior Battery Systems
Lead acid batteries typically comprise a series of thin, flat, generally rectangular grids for carrying a current through the battery. The grids also serve as a substrate for supporting electrochemically active materials or "paste" deposited thereon during manufacture to form battery plates. The paste typically comprises a mixture of lead oxide and a dilute acid solution, for example sulfuric acid. The paste composition is determined by power requirements, cost and the battery environment, as is known in the art.
It is also known that groupings of individual battery plates may be assembled, interleaved with separator material, and cast together to form plate stacks. The latter are then assembled in a container to form a final battery. A typical example would be an automobile battery of the 12-volt variety where, six individual stacks are placed into a plastic container having six compartments. Obviously, to permit current to flow throughout the battery, it is necessary to join the cast-on straps of one stack with the appropriate cast-on strap of the adjacent stack. Moreover, it is necessary to provide terminal electrodes which will extend through the casing to permit electrical contact with the vehicle's electrical system.
After the battery plates are fully assembled, they are formed, i.e. charged, and the battery is placed into service. An important characteristic of batteries is called "cold cranking power," i.e. the amount of power which can be generated per unit of time. Further references will be made to cold cranking power in later sections of this specification.
In more recent years, the grid has been formed in a screen-like pattern, having a matrix or a honeycomb pattern of alternating metal strips and open spaces. A porous chemical paste is applied to the grids and the lead frame members at the top, bottom and sides. After the paste is cured, the electrodes are assembled into a battery casing, whereupon the housing is filled with aqueous electrolyte solution and sealed. In current systems, the lugs have been symmetrically offset from the centerline of the battery by amounts ranging from 1/2 inch to much larger amounts, and in many designs, the lugs of either the positive or negative battery plates are located near an upper corner of the plate. During assembly, it is necessary to couple together the positive lugs of the battery plates and to couple together the lugs of the negative plates. This is typically accomplished using cast-on lead straps formed by taking assembled battery plate stacks, inverting them, and dipping the lugs into molten lead contained within a mold. In the most common batteries in use at the time of the filing of this specification, such cast-on straps have an upstanding end position, as will be explained more fully when the drawings are described later herein.
Several of these basic battery principles are illustrated in United States patents which will be discussed below. The first is U.S. Pat. No. 669,085, issued Mar. 5, 1901 to Heidel and entitled "Battery Electrode." This patent relates to a method of mounting battery grids in a container, where recessed bosses are provided around the edges of the battery and plugs are seated in the bosses to serve as insulating spacers between the electrode and the battery cell. In FIG. 1 of the patent, an element which is unnumbered appears to be relatively near but is offset from the centerline of the battery. The element appears to be pasted, which would make it entirely distinct from the types of collector systems used today.
Another battery storage plate is shown in U.S. Pat. No. 3,466,193, issued Sep. 9, 1969 to Hughel and entitled "Storage Battery Positive Plate With Lead Fibers." In this device, 5-25% of short lead fibers are used with the positive paste material. The collectors shown in this device extend from the edges of the grids.
In U.S. Pat. No. 3,923,545, issued Dec. 2, 1975 to Margulies, et al., a "Grid Structure For High Rate Lead/Acid Battery" is described. In this device, the grid is constructed of more numerous vertical elements than horizontal elements and a collector tab is provided offset from the center of the top. A tapered portion is provided on the top frame element. In addition, at least two current-carrying grid elements are tapered in width and expand from the bottom of the plate toward the top thereof, the purpose of which is stated to be to maximize mechanical support while minimizing the resistive paths in regions of highest current density. In the background section of this patent, reference is made to an earlier patent wherein the tops of several "bars" nearest the terminal are thickened to provide ample current-carrying capacity in the region of the terminal lug.
Another earlier grid design is shown in U.S. Pat. No. 4,118,553, issued Oct. 3, 1978 to Buckethal, et al. and entitled "Composite Battery Plate Grid And Method Of Manufacturing." This patent, owned by the assignee of the present invention, describes a composite grid including a plastic support having conductive members cast in a pattern extending generally radially from the collector lug, which in this patent is located near a corner of the grid. The grid includes a rectangular frame, and horizontal and vertical grid elements, as well as the radial elements previously mentioned. The patent relates primarily to methods for molding the grid, especially the plastic support thereof.
In U.S. Pat. No. 4,221,852, issued Sep. 9, 1980 to Qureshi for "Radial Grids For Lead Acid Batteries," the storage grid is described as including a frame having a lug on the upper edge near the corner, a set of wires parallel to one another connecting the side frame elements and a set of radial arms diverging away from the upper edge to connect the upper edge to each of the three other edges of the frame. From the patent drawings, it appears that the radial and horizontal arms are generally uniform in cross-section, although the pattern of open spaces varies as the radial arms tend to converge toward the top of the grid. Several embodiments of the radial wire design are shown.
A different grid arrangement for lead acid batteries is shown in U.S. Pat. No. 4,320,183, issued Mar. 16, 1982 to Qureshi and entitled "Grid For Batteries." The grid disclosed in this patent for supporting the active battery material is characterized by a "quasi-radial design" adapted to provide efficient battery operation. In addition to the horizontal grid elements and straight radial elements emanating from the upper frame, the design includes several elements which are partially radial and partially vertical in configuration. The obliquely arranged wires extend toward the bottom frame element.
Yet a different arrangement for grid elements is disclosed in Anderson, et al., U.S. Pat. No. 4,555,459, issued Nov. 26, 1985 and entitled "Battery Grids." The horizontal and angled wires defining this grid form a plurality of parallelogram spaces of substantially equal size, whereby paste pellets may be more uniform in the pasting operation. The lug is located on the top frame generally adjacent a corner, and in one embodiment, a tapered wire element is arranged vertically with the taper extending from bottom to top to divide the grid into two rectangular sections, each of which contains the parallelogram spaces.
A different battery plate configuration is shown in U.S. Pat. No. 4,683,180, issued Jul. 28, 1987 to Bish, et al. and entitled "Electric Storage Battery." The lugs for the respective positive and negative grids are each offset from the centerline of the battery and are coupled to like plates using a device which includes an insulating collar tightly engaging the root of each lug. The collars of the several plates abut one another and may serve to form a mold for shaping a plate strap cast thereon. The lug itself is depicted as being generally rectangular at its upper end and generally trapezoidal in the portion intermediate the upper portion and the grid itself.
Finally, another battery grid is disclosed in U.S. Pat. No. 5,098,799, issued Mar. 24, 1992 to Bowen, et al. and entitled "Battery Electrode Growth Accommodation." In this device, a battery grid includes a plastic frame and a plate suspended from the top of the frame to hang freely in the plastic frame. The suspension mechanism permits expansion of the paste in the planar direction of the grid. The grid itself is a relatively standard design, with a lug offset from the center of the upper frame member, with horizontal wires and a plurality of radially extending wires.
While it is apparent from the foregoing description that numerous plate and grid designs have been developed in the lead acid battery art, several problems still remain in the design and manufacture of such batteries. One of the most significant problems is the weight associated with this type of energy source, especially in these times of increasing concern for fuel efficiency and maintaining components at their lowest possible weight. Most commercial battery plates include lead alloy grid materials, combined with the electrolyte and lead based paste materials. Any system which reduced the battery weight, while maintaining the power required for a particular application, would be a significant advance in the art.
Further problems relate to the manufacture of such batteries, where the plates must be coupled by cast-on straps and where the straps must be welded to one another in adjacent cells to permit current flow through the system. Ways in which such manufacturing problems could be overcome would also represent a significant advance in the art.
Furthermore, it is always advantageous to look for ways to maximize the efficiency of the grid in transferring current from the sites where the electrochemical reactions are occurring to the collector lugs. Improvement in grid design in this area is also important.
Any system which combines the various advantages discussed in the previous few paragraphs would represent a very substantial advance in this art.